Communication system and concentrator

ABSTRACT

A communication system of the present invention includes a user equipment (UE), and a plurality of cells that perform communication with the UE. The plurality of cells include a macro cell having a relatively-wide-range coverage, and a plurality of small cells having a relatively-narrow-range coverage. The plurality of small cells are connected to a concentrator. The concentrator selects the small cell to which the UE is to be connected, from among a plurality of small cells, based on the flow of at least either one of the received data that each small cell receives from the UE and the transmission data that each small cell transmits to an MME and an S-GW.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. § 120 from U.S. application Ser. No. 14/903,519, filedJan. 7, 2016, the entire contents of which is incorporated herein byreference and which is a national stage of International Application No.PCT/JP2014/064904, filed Jun. 5, 2014, which is based upon and claimsthe benefit of priority under 35 U.S.C. § 119 from Japanese PatentApplication No. 2013-148201, filed Jul. 17, 2013.

TECHNICAL FIELD

The present invention relates to a communication system that performsradio communication between a communication terminal device and a basestation device.

BACKGROUND ART

The 3rd generation partnership project (3GPP) that is a standardorganization regarding a mobile communication system is studying newcommunication systems referred to as long term evolution (LTE) regardingradio sections and system architecture evolution (SAE) regarding theoverall system configuration including a core network and a radio accessnetwork (hereinafter, collectively referred to as a network as well).This communication system is also referred to as 3.9 generation (3.9 G)system.

As an access scheme of the LTE, orthogonal frequency divisionmultiplexing (OFDM) is used in a downlink direction, and single carrierfrequency division multiple access (SC-FDMA) is used in an uplinkdirection. Further, differently from wideband code division multipleaccess (W-CDMA), circuit switching is not provided but a packetcommunication system is only provided in the LTE.

The current decisions by 3GPP regarding the frame configuration in theLTE system described in Non-Patent Document 1 (Chapter 5) will bedescribed with reference to FIG. 1. FIG. 1 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 1, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal (SS) per each radio frame. Thesynchronization signals are classified into a primary synchronizationsignal (P-SS) and a secondary synchronization signal (S-SS).

Non-Patent Document 1 (Chapter 5) describes the current decisions by3GPP regarding the channel configuration in the LTE system. It isassumed that the same channel configuration is used in a closedsubscriber group (CSG) cell as that of a non-CSG cell. The CSG cell willbe described below (see Chapter 3.1 of Non-Patent Document 2).

A physical broadcast channel (PBCH) is a channel for downlinktransmission from a base station to a mobile terminal. A BCH transportblock is mapped to four subframes within a 40 ms interval. There is noexplicit signaling indicating 40 ms timing.

A physical control format indicator channel (PCFICH) is a channel fordownlink transmission from the base station to the mobile terminal. ThePCFICH notifies the number of OFDM (Orthogonal Frequency DivisionMultiplexing) symbols used for PDCCHs from the base station to themobile terminal. The PCFICH is transmitted in each subframe.

A physical downlink control channel (PDCCH) is a channel for downlinktransmission from the base station to the mobile terminal. The PDCCHnotifies the resource allocation information for a downlink sharedchannel (DL-SCH) being one of the transport channels described later,resource allocation information for a paging channel (PCH) being one ofthe transport channels described later, and HARQ (Hybrid AutomaticRepeat reQuest) information related to DL-SCH. The PDCCH carries anuplink scheduling grant. The PDCCH carries acknowledgement(Ack)/negative acknowledgement (Nack) that is a response signal touplink transmission. The PDCCH is referred to as an L1/L2 control signalas well.

A physical downlink shared channel (PDSCH) is a channel for downlinktransmission from the base station to the mobile terminal. A downlinkshared channel (DL-SCH) that is a transport channel and a PCH that is atransport channel are mapped to the PDSCH.

A physical multicast channel (PMCH) is a channel for downlinktransmission from the base station to the mobile terminal. A multicastchannel (MCH) that is a transport channel is mapped to the PMCH.

A physical uplink control channel (PUCCH) is a channel for uplinktransmission from the mobile terminal to the base station. The PUCCHcarries Ack/Nack that is a response signal to downlink transmission. ThePUCCH carries a channel quality indicator (CQI) report. The CQI isquality information indicating the quality of received data or channelquality. In addition, the PUCCH carries a scheduling request (SR).

A physical uplink shared channel (PUSCH) is a channel for uplinktransmission from the mobile terminal to the base station. An uplinkshared channel (UL-SCH) that is one of the transport channels is mappedto the PUSCH.

A physical hybrid ARQ indicator channel (PHICH) is a channel fordownlink transmission from the base station to the mobile terminal. ThePHICH carries Ack/Nack that is a response signal to uplink transmission.A physical random access channel (PRACH) is a channel for uplinktransmission from the mobile terminal to the base station. The PRACHcarries a random access preamble.

A downlink reference signal (RS) is a known symbol in the LTEcommunication system. The following five types of downlink referencesignals are defined: cell-specific reference signals (CRS), MBSFNreference signals, data demodulation reference signal (DM-RS) beingUE-specific reference signals, positioning reference signals (PRS), andchannel-state information reference signals (CSI-RS). The physical layermeasurement objects of a mobile terminal include reference signalreceived power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)will be described. A broadcast channel (BCH) among the downlinktransport channels shown in FIG. 5(A) is broadcast to the entirecoverage of a base station (cell). The BCH is mapped to the physicalbroadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH can be broadcasted to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a mobile terminal for enabling themobile terminal to save power. The DL-SCH is mapped to the physicaldownlink shared channel (PDSCH).

The paging channel (PCH) supports DRX of the mobile terminal forenabling the mobile terminal to save power. The PCH is required to bebroadcast to the entire coverage of the base station (cell). The PCH ismapped to physical resources such as the physical downlink sharedchannel (PDSCH) that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of MBMSservices (MTCH and MCCH) in multi-cell transmission. The MCH supportssemi-static resource allocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH) among the uplink transport channels. TheUL-SCH supports dynamic or semi-static resource allocation. The UL-SCHis mapped to the physical uplink shared channel (PUSCH).

A random access channel (RACH) is limited to control information. TheRACH involves a collision risk. The RACH is mapped to the physicalrandom access channel (PRACH).

The HARQ will be described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest (ARQ) and error correction (forward error correction). The HARQis advantageous in that error correction functions effectively byretransmission even for a channel whose communication quality changes.In particular, it is also possible to achieve further qualityimprovement in retransmission through combination of the receptionresults of the first transmission and the reception results of theretransmission.

An example of the retransmission method will be described. If thereceiver fails to successfully decode the received data, in other words,if a cyclic redundancy check (CRC) error occurs (CRC=NG), the receivertransmits “Nack” to the transmitter. The transmitter that has received“Nack” retransmits the data. If the receiver successfully decodes thereceived data, in other words, if a CRC error does not occur (CRC=OK),the receiver transmits “AcK” to the transmitter. The transmitter thathas received “Ack” transmits the next data.

The logical channels described in Non-Patent Document 1 (Chapter 6) willbe described. A broadcast control channel (BCCH) is a downlink channelfor broadcast system control information. The BCCH that is a logicalchannel is mapped to the broadcast channel (BCH) or downlink sharedchannel (DL-SCH) that is a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging information and system information change notifications. The PCCHis used when the network does not know the cell location of a mobileterminal. The PCCH that is a logical channel is mapped to the pagingchannel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between mobile terminals and a base station. The CCCH isused in the case where the mobile terminals have no RRC connection withthe network. In a downlink direction, the CCCH is mapped to the downlinkshared channel (DL-SCH) that is a transport channel. In an uplinkdirection, the CCCH is mapped to the uplink shared channel (UL-SCH) thatis a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to amobile terminal. The MCCH is used only by a mobile terminal duringreception of the MBMS. The MCCH is mapped to the multicast channel (MCH)that is a transport channel.

A dedicated control channel (DCCH) is a channel that transmits dedicatedcontrol information between a mobile terminal and a network on apoint-to-point basis. The DCCH is used if the mobile terminal has an RRCconnection. The DCCH is mapped to the uplink shared channel (UL-SCH) inuplink and mapped to the downlink shared channel (DL-SCH) in downlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicated mobileterminal. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a mobile terminal. The MTCH is achannel used only by a mobile terminal during reception of the MBMS. TheMTCH is mapped to the multicast channel (MCH).

A CGI represents a cell global identifier. An ECGI represents an E-UTRANcell global identifier. A closed subscriber group (CSG) cell isintroduced in the LTE, and the long term evolution advanced (LTE-A) anduniversal mobile telecommunication system (UMTS) described below.

The closed subscriber group (CSG) cell is a cell in which subscriberswho are allowed to use are specified by an operator (hereinafter, alsoreferred to as a “cell for specific subscribers”). The specifiedsubscribers are allowed to access one or more cells of a public landmobile network (PLMN). One or more cells in which the specifiedsubscribers are allowed access are referred to as “CSG cell(s).” Notethat access is limited in the PLMN.

The CSG cell is part of the PLMN that broadcasts a specific CSG identity(CSG ID; CSG-ID) and broadcasts “TRUE” in a CSG indication. Theauthorized members of the subscriber group who have registered inadvance access the CSG cells using the CSG-ID that is the accesspermission information.

The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDsexist in the LTE communication system. The CSG-IDs are used by mobileterminals (UEs) for making access from CSG-related members easier.

The locations of mobile terminals are tracked on the basis of an areacomposed of one or more cells. The locations are tracked for enablingtracking the locations of mobile terminals and calling mobile terminals,in other words, incoming calling to mobile terminals even in an idlestate. An area for tracking locations of mobile terminals is referred toas a tracking area.

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation, or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 3 discloses three different modes ofthe access to the HeNB and HNB. Specifically, an open access mode, aclosed access mode, and a hybrid access mode are disclosed.

The respective modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a CSG cell where only CSG members are allowedaccess. In the hybrid access mode, the HeNB and HNB are operated as CSGcells where non-CSG members are allowed access at the same time. Inother words, a cell in the hybrid access mode (also referred to as ahybrid cell) is the cell that supports both the open access mode and theclosed access mode.

In 3GPP, among all physical cell identifiers (PCI), there is a range ofPCIs reserved by the network for use by CSG cells (see Chapter 10.5.1.1of Non-Patent Document 1). Division of the PCI range is also referred toas PCI split. The information about PCI split (also referred to as PCIsplit information) is broadcast in the system information from a basestation to mobile terminals being served thereby. To be served by a basestation means to take the base station as a serving cell.

Non-Patent Document 4 discloses the basic operation of a mobile terminalusing PCI split. The mobile terminal that does not have the PCI splitinformation needs to perform cell search using all PCIs, for example,using all 504 codes. On the other hand, the mobile terminal that has thePCI split information is capable of performing cell search using the PCIsplit information.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Documents 5 and 6). TheLTE-A is based on the LTE communication system regarding radio sectionsand is configured by addition of several new techniques thereto.

Carrier aggregation (CA) is studied in the LTE-A system, in which two ormore component carriers (CCs) are aggregated to support widertransmission bandwidths up to 100 MHz.

In the case where a CA is configured, a UE has a single RRC connectionwith a network (NW). In RRC connection, one serving cell provides NASmobility information and security input. This cell is referred to as aprimary cell (PCell). In downlink, a carrier corresponding to a PCell isa downlink primary component carrier (DL PCC). In uplink, a carriercorresponding to PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a serving cell group witha PCell, in accordance with the UE capability. In downlink, a carriercorresponding to SCell is a downlink secondary component carrier (DLSCC). In uplink, a carrier corresponding to SCell is an uplink secondarycomponent carrier (UL SCC).

A serving cell group of one PCell and one or more SCells is configuredfor one UE.

Further, new techniques in the LTE-A include the technique of supportingwider bands (wider bandwidth extension) and the coordinated multiplepoint transmission and reception (CoMP) technique. The CoMP studied forLTE-A in 3GPP is described in Non-Patent Document 7.

Further, 3GPP is pursuing specifications standard of Release 12. Amongthe specifications, in order to satisfy a tremendous volume of trafficin the future, the use of small eNBs configuring a small cell isstudied. Examples of the study include the technique of increasingspectral efficiency by configuring a large number of small cells byinstalling a large number of small eNBs to increase communicationcapacity.

A traffic amount of a mobile network is in an increasing tendency, andincreasing a communication speed is also progressed. When theapplication of the LTE and the LTE-A is started on a full scale, thecommunication speed is further increased, and an increase of the trafficamount is expected.

A conventional mobile communication system has a problem that theprobability of occurrence of a delay in the network and loss of data mayfurther increase (hereinafter, also referred to as an “occurrenceprobability”) as a traffic amount increases. A technique to solve such aproblem is disclosed in Patent Document 1, for example.

Patent Document 1 discloses a user device having means for selecting adata transmission cell based on a measurement value of a congestionlevel in a cell.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Patent Application Laid-Open No.    2003-134550

Non-Patent Documents

-   Non-Patent Document 1: 3GPP TS 36.300 V11.4.0-   Non-Patent Document 2: 3GPP TS 36.304 V11.1.0 Chapter 3.1-   Non-Patent Document 3: 3GPP S1-083461-   Non-Patent Document 4: 3GPP R2-082899-   Non-Patent Document 5: 3GPP TR 36.814 V9.0.0-   Non-Patent Document 6: 3GPP TR 36.912 V10.0.0-   Non-Patent Document 7: 3GPP TR 36.819 V11.1.0

SUMMARY OF INVENTION Problems to be Solved by the Invention

According to the technique disclosed in Patent Document 1, a user deviceselects a cell. In the case where a plurality of user devices exist inthe communication system, the user devices select cells individually. Inthis case, there is a risk that a cell having a relatively lowcongestion level at a time point of measuring the congestion level isselected by a plurality of user devices so that load of the cellincreases. Thus, with the technique disclosed in Patent Document 1, itis not possible to reduce the occurrence probability of a delay in thenetwork and the loss of data.

Further, according to the technique disclosed in Patent Document 1, theuser device selects a cell having a low congestion level in downlink.Patent Document 1 fails to expressly disclose uplink. With the techniquedisclosed in Patent Document 1, it is not possible to select a cell inconsideration of congestion in uplink.

An object of the present invention is to provide a communication systemcapable of reducing the occurrence probability of a delay in the networkand loss of data.

Means for Solving the Problems

A communication system according to the present invention includes acommunication terminal device, and one or a plurality of base stationdevices that perform radio communication with the communication terminaldevice. The communication system includes a plurality of cells that areconfigured by the one or the plurality of base station devices, andperform radio communication with the communication terminal device bybeing connected to the communication terminal device, and a higher-leveldevice that is provided in a higher level of the base station device. Acell to which the communication terminal device is to be connected isselected from among the plurality of cells, based on a flow of at leasteither one of received data that each cell has received from thecommunication terminal device and transmission data that each cell hastransmitted to the higher-level device.

Effects of the Invention

According to the communication system of the present invention, a cellto which the communication terminal device is to be connected isselected from among the plurality of cells, based on a flow of at leasteither one of received data that each cell has received from thecommunication terminal device and transmission data that each cell hastransmitted to the higher-level device. Accordingly, in the case where atraffic volume in the communication system has increased, load can bedispersed to each cell. Therefore, because concentration of traffic in aspecific cell can be prevented, it is possible to reduce the occurrenceprobability of a delay in the entire network including a core networkand loss of data.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a radio frame usedin an LTE communication system.

FIG. 2 is a block diagram showing the overall configuration of an LTEcommunication system 700 currently under discussion of 3GPP.

FIG. 3 is a block diagram showing the configuration of a user equipment71 of FIG. 2 being a user equipment according to the present invention.

FIG. 4 is a block diagram showing the configuration of a base station 72of FIG. 2 being a base station according to the present invention.

FIG. 5 is a block diagram showing the configuration of an MME accordingto the present invention.

FIG. 6 is a flowchart showing an outline from a cell search to an idlestate operation performed by a user equipment (UE) in the LTEcommunication system.

FIG. 7 is a diagram showing the concept of the configuration of cells inwhich macro eNBs and small eNBs coexist.

FIG. 8 is a block diagram showing the configuration of a communicationsystem 1400 according to a first embodiment of the present invention.

FIG. 9 is a diagram showing a flow direction of data in thecommunication system 1400 according to the first embodiment of thepresent invention.

FIG. 10 is a diagram showing a configuration of a protocol stack in acommunication system 1410 according to a conventional technique.

FIG. 11 is a diagram showing the configuration of a protocol stack inthe communication system 1400 according to the first embodiment of thepresent invention.

FIG. 12 is a block diagram showing the configuration of a communicationsystem 1500 according to a second embodiment of the present invention.

FIG. 13 is a block diagram showing the configuration of a communicationsystem 1600 according to a third embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 2 is a block diagram showing an overall configuration of an LTEcommunication system 700, which is currently under discussion of 3GPP.FIG. 2 will be described. A radio access network will be referred to asan evolved universal terrestrial radio access network (E-UTRAN) 70. Amobile terminal device (hereinafter, referred to as a “mobile terminal(user equipment (UE))” 71 being a communication terminal device iscapable of performing radio communication with a base station device(hereinafter, referred to as a “base station (E-UTRAN NodeB: eNB)” 72,and transmits and receives signals through radio communication.

A control protocol RRC between the user equipment 71 and the basestation 72 performs broadcast, paging, RRC connection management, andthe like. The states of the base station 72 and the user equipment 71 inRRC are classified into RRC_IDLE and RRC_CONNECTED.

In RRC_IDLE, public land mobile network (PLMN) selection, systeminformation (SI) broadcast, paging, cell re-selection, mobility, and thelike are performed. In RRC_CONNECTED, the user equipment has RRCconnection and is capable of transmitting/receiving data to/from anetwork. In RRC_CONNECTED, for example, handover (HO) and measurement ofa neighbor cell are performed.

The base stations 72 are classified into eNBs 76 and Home-eNBs 75. Thecommunication system 700 includes an eNB group 72-1 including aplurality of eNBs 76, and a Home-eNB group 72-2 including a plurality ofHome-eNBs 75. A system configured by an EPC (Evolved Packet Core) beinga core network and an E-UTRAN 70 being a radio access network will bereferred to as an EPS (Evolved Packet System). The EPC being a corenetwork and the E-UTRAN 70 being the radio access network are alsocollectively referred to as a “network”.

The eNB 76 is connected to an MME/S-GW unit (hereinafter, also referredto as an “MME unit”) 73 including an MME, or an S-GW, or an MME and anS-GW by means of an S1 interface, and control information iscommunicated between the eNB 76 and the MME unit 73. A plurality of MMEunits 73 may be connected to one eNB 76. The eNBs 76 are connected toeach other by means of an X2 interface, and control information iscommunicated between the eNBs 76.

The Home-eNB 75 is connected to the MME unit 73 by means of an S1interface, and control information is communicated between the Home-eNB75 and the MME unit 73. A plurality of Home-eNBs 75 are connected to oneMME unit 73. Alternatively, the Home-eNBs 75 are connected to the MMEunits 73 through a HeNBGW (Home-eNB GateWay) 74. The Home-eNB 75 isconnected to the HeNBGW 74 by an S1 interface, and the HeNBGW 74 isconnected to the MME unit 73 by means of an S1 interface.

One or a plurality of Home-eNBs 75 are connected to one HeNBGW 74, andinformation is communicated therebetween by means of an S1 interface.The HeNBGW 74 is connected to one or a plurality of MME units 73, andinformation is communicated therebetween by means of an S1 interface.

The MME units 73 and HeNBGW 74 are higher-level devices, specifically,higher nodes, and control connections between the eNB 76 and theHome-eNB 75 being base stations, and the user equipment (UE) 71. The MMEunit 73 configures an EPC being a core network. The base station 72 andthe HeNBGW 74 configure the E-UTRAN 70.

Further, 3GPP has studied the configuration below. The X2 interfacebetween the Home-eNBs 75 is supported. In other words, the Home-eNBs 75are connected to each other by means of an X2 interface, and controlinformation is communicated between the Home-eNBs 75. The HeNBGW 74appears to the MME unit 73 as the Home-eNB 75. The HeNBGW 74 appears tothe Home-eNB 75 as the MME unit 73.

The interfaces between the Home-eNBs 75 and the MME units 73 are thesame, which are the S1 interfaces, in the both cases where the Home-eNB75 is connected to the MME unit 73 through the HeNBGW 74 and theHome-eNB 75 is directly connected to the MME unit 73.

The base station device 72 may configure a single cell, or may configurea plurality of cells. Each cell has a range predetermined as a coveragein which the cell can communicate with a communication terminal device,and the cell performs radio communication with the communicationterminal device within the coverage. In the case where one base stationdevice configures a plurality of cells, every cell is configured tocommunicate with a mobile terminal.

FIG. 3 is the block diagram showing the configuration of the userequipment 71 of FIG. 2 being a user equipment according to the presentinvention. The transmission process of the user equipment 71 illustratedin FIG. 3 will be described. First, a transmission data buffer unit 803stores the control data from a protocol processing unit 801 and the userdata from an application unit 802. The data stored in the transmissiondata buffer unit 803 is passed to an encoding unit 804 and is subjectedto an encoding process such as error correction. There may exist thedata output from the transmission data buffer unit 803 directly to amodulating unit 805 without the encoding process. The data encoded bythe encoding unit 804 is modulated by the modulating unit 805. Themodulated data is converted into a baseband signal, and the basebandsignal is output to a frequency converting unit 806 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 807 to the basestation 72.

The user equipment 71 executes the reception process as follows. Theradio signal from the base station 72 is received through the antenna807. The received signal is converted from a radio reception frequencyinto a baseband signal by the frequency converting unit 806 and is thendemodulated by a demodulating unit 808. The demodulated data is passedto a decoding unit 809 and is subjected to a decoding process such aserror correction. Among the pieces of decoded data, the control data ispassed to the protocol processing unit 801, while the user data ispassed to the application unit 802. A series of processes of the userequipment 71 is controlled by a control unit 810. This means that,though not illustrated in FIG. 3, the control unit 810 is connected tothe respective units 801 to 809.

FIG. 4 is a block diagram showing the configuration of the base station72 of FIG. 2 being a base station according to the present invention.The transmission process of the base station 72 illustrated in FIG. 4will be described. An EPC communication unit 901 performs datatransmission and reception between the base station 72 and the EPC (suchas the MME unit 73) and the HeNBGW 74. A communication with another basestation unit 902 performs data transmission and reception to and fromanother base station. The EPC communication unit 901 and thecommunication with another base station unit 902 each transmit andreceive information to and from a protocol processing unit 903. Thecontrol data from the protocol processing unit 903, and the user dataand control data from the EPC communication unit 901 and thecommunication with another base station unit 902 are stored in atransmission data buffer unit 904.

The data stored in the transmission data buffer unit 904 is passed to anencoding unit 905 and is then subjected to an encoding process such aserror correction. There may exist the data output from the transmissiondata buffer unit 904 directly to a modulating unit 906 without theencoding process. The encoded data is modulated by the modulating unit906. The modulated data is converted into a baseband signal, and thebaseband signal is output to a frequency converting unit 907 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 908 to one or aplurality of user equipments 71.

The reception process of the base station 72 is executed as follows. Aradio signal from one or a plurality of user equipments 71 is receivedthrough the antenna 908. The received signal is converted from a radioreception frequency into a baseband signal by the frequency convertingunit 907, and is then demodulated by a demodulating unit 909. Thedemodulated data is passed to a decoding unit 910 and is then subjectedto a decoding process such as error correction. Among the pieces ofdecoded data, the control data is passed to the protocol processing unit903, the EPC communication unit 901, or the communication with anotherbase station unit 902, while the user data is passed to the EPCcommunication unit 901 and the communication with another base stationunit 902. A series of processes by the base station 72 is controlled bya control unit 911. This means that, though not illustrated in FIG. 4,the control unit 911 is connected to the respective units 901 to 910.

FIG. 5 is a block diagram showing the configuration of the MME accordingto the present invention. FIG. 5 illustrates the configuration of an MME73 a included in the MME unit 73 illustrated in FIG. 2 described above.A PDN GW communication unit 1001 performs data transmission andreception between the MME 73 a and a PDN GW. A base stationcommunication unit 1002 performs data transmission and reception betweenthe MME 73 a and the base station 72 by means of the S1 interface. Ifthe data received from the PDN GW is user data, the user data is passedfrom the PDN GW communication unit 1001 to the base stationcommunication unit 1002 via a user plane communication unit 1003 and isthen transmitted to one or a plurality of base stations 72. If the datareceived from the base station 72 is user data, the user data is passedfrom the base station communication unit 1002 to the PDN GWcommunication unit 1001 via the user plane communication unit 1003 andis then transmitted to the PDN GW.

If the data received from the PDN GW is control data, the control datais passed from the PDN GW communication unit 1001 to a control planecontrol unit 1005. If the data received from the base station 72 iscontrol data, the control data is passed from the base stationcommunication unit 1002 to the control plane control unit 1005.

A HeNBGW communication unit 1004 is provided in the case where theHeNBGW 74 is provided, which performs data transmission and receptionbetween the MME 73 a and the HeNBGW 74 by means of the interface (IF)according to an information type. The control data received from theHeNBGW communication unit 1004 is passed from the HeNBGW communicationunit 1004 to the control plane control unit 1005. The processing resultsof the control plane control unit 1005 are transmitted to the PDN GW viathe PDN GW communication unit 1001. The processing results of thecontrol plane control unit 1005 are transmitted to one or a plurality ofbase stations 72 by means of the S1 interface via the base stationcommunication unit 1002, and are transmitted to one or a plurality ofHeNBGWs 74 via the HeNBGW communication unit 1004.

The control plane control unit 1005 includes a NAS security unit 1005-1,an SAE bearer control unit 1005-2, an idle state mobility managing unit1005-3, or other unit, and performs an overall process for the controlplane. The NAS security unit 1005-1 provides, for example, security of anon-access stratum (NAS) message. The SAE bearer control unit 1005-2manages, for example, a system architecture evolution (SAE) bearer. Theidle state mobility managing unit 1005-3 performs, for example, mobilitymanagement of an idle state (LTE-IDLE state, which is merely referred toas idle as well), generation and control of a paging signal in the idlestate, addition, deletion, update, and search of a tracking area of oneor a plurality of user equipments 71 being served thereby, and trackingarea list management.

The MME 73 a distributes a paging signal to one or a plurality of basestations 72. In addition, the MME 73 a performs mobility control of anidle state. When the user equipment is in the idle state and an activestate, the MME 73 a manages a list of tracking areas. The MME 73 abegins a paging protocol by transmitting a paging message to the cellbelonging to a tracking area in which the UE is registered. The idlestate mobility managing unit 1005-3 may manage the CSG of the Home-eNBs75 to be connected to the MME 73 a, the CSG-IDs, and a whitelist.

An example of a cell search method in a mobile communication system willbe described next. FIG. 6 is the flowchart showing an outline from acell search to an idle state operation performed by a user equipment(UE) in the LTE communication system. When starting a cell search, inStep ST1201, the user equipment synchronizes slot timing and frametiming by a primary synchronization signal (P-SS) and a secondarysynchronization signal (S-SS) transmitted from a neighbor base station.

The P-SS and S-SS are collectively referred to as a synchronizationsignal (SS). Synchronization codes, which individually correspond tophysical cell identities (PCIs) assigned per cell, are assigned to thesynchronization signal (SS). The number of PCIs is currently studied in504 ways. The 504 ways of PCIs are used for synchronization, and thePCIs of the synchronized cells are detected (specified).

In Step ST1202, next, with respect to the synchronized cells, the userequipment detects a cell-specific reference signal (CRS) being areference signal (RS) transmitted from the base station per cell andmeasures the reference signal received power (RSRP). The codesindividually corresponding to the PCIs are used for the reference signalRS. Separation from another cell is enabled by correlation using thecode. The code for RS of the cell is derived from the PCI specified inStep ST1201, which makes it possible to detect the RS and measure the RSreceived power.

In Step ST1203, next, the user equipment selects the cell having thebest RS reception quality, for example, the cell having the highest RSreceived power, that is, the best cell, from one or more cells that havebeen detected up to Step ST1202.

In Step ST1204, next, the user equipment receives the PBCH of the bestcell and obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas transmission bandwidth configuration (dl-bandwidth)), the number oftransmission antennas, and system frame number (SFN).

In Step ST1205, next, the user equipment receives the DL-SCH of the cellon the basis of the cell configuration information of the MIB, tothereby obtain a system information block (SIB) 1 of the broadcastinformation BCCH. The SIB1 contains information about the access to thecell, information about cell selection, and scheduling information onother SIB (SIBk; k is an integer equal to or larger than two). Inaddition, the SIB1 contains a tracking area code (TAC).

In Step ST 1206, next, the user equipment compares the TAC of the SIB1received in Step ST 1205 with the TAC portion of a tracking areaidentifier (TAI) in the tracking area list that has already beenpossessed by the user equipment. The tracking area list is also referredto as a TAI list. The TAI is identification information for identifyinga tracking area, and is composed of an MCC (Mobile Country Code), an MNC(Mobile Network Code), and a TAC (Tracking Area Code). MCC is a countrycode. MNC is a network code. TAC is the code number of a tracking area.

If the TAC received in Step ST1205 is identical to the TAC included inthe tracking area list as a result of the comparison of Step ST1206, theuser equipment enters an idle state operation in the cell. If the TACreceived in Step ST1205 is not included in the tracking area list as aresult of the comparison, the user equipment requires a core network(EPC) including MME and the like to change a tracking area through thecell for performing tracking area update (TAU).

A device that configures a core network (hereinafter, also referred toas a “core network side device”) updates the tracking area list on thebasis of an identification number (such as a UE-ID) of the userequipment transmitted from the user equipment together with a TAUrequest signal. The core network side device transmits the updatedtracking area list to the user equipment. The user equipment rewrites(updates) the TAC list of the user equipment on the basis of thereceived tracking area list. After that, the user equipment enters theidle state operation in the cell.

Widespread use of smartphones and tablet terminals explosively increasestraffic in cellular radio communications, causing a fear of insufficientradio resources all over the world. To increase spectral efficiency,accordingly, it is studied to downsize cells for further spatialseparation.

In the configuration of a conventional cell, a cell configured by an eNBhas a relatively-wide-range coverage. Conventionally, a cell isconfigured such that relatively-wide-range coverages of a plurality ofcells configured by a plurality of eNBs cover a certain area.

In the case of the downsized cells, the cell configured by an eNB has anarrow-range coverage as compared with the coverage of a cell configuredby a conventional eNB. Therefore, in order to cover a certain area as inthe conventional case, a larger number of downsized eNBs than theconventional eNBs are necessary.

In the following description, like the cell configured by a conventionaleNB, a cell configuring a relatively-wide-range coverage, that is, acell having a relatively wide coverage area, will be referred to as a“macro cell”, and an eNB that configures the macro cell will be referredto as a “macro eNB”. Further, like a downsized cell that configures arelatively-narrow-range coverage, that is, a cell having a relativelynarrow coverage area will be referred to as a “small cell”, and an eNBconfiguring the small cell will be referred to as a “small eNB”.

The macro eNB may be, for example, a “wide area base station” describedin 3GPP TS 36.141 V11.1.0 (hereinafter, referred to as “Non-PatentDocument 8”).

The small eNB may be, for example, a low power node, local area node, orhotspot. Alternatively, the small eNB may be a pico eNB configuring apico cell, a femto eNB constituting a femto cell, HeNB, RRH, RRU, RRE,or RN. Still alternatively, a small eNB may be a “local area basestation”, or a “home base station” as described in Non-Patent Document8.

FIG. 7 is a diagram showing the concept of the configuration of cells inwhich macro eNBs and small eNBs coexist. A macro cell configured by amacro eNB has a relatively-wide-range coverage 1301. A small cellconfigured by small eNBs has a narrow range coverage 1302 as comparedwith the coverage 1301 of a macro cell configured by macro eNBs.

In the case where a plurality of eNBs coexist, a coverage of a cellconfigured by a certain eNB may be included in the coverage of a cellconfigured by other eNB. In the configuration of a cell illustrated inFIG. 7, as indicated by a reference “1304” or “1305”, the coverage 1302of a small cell configured by small eNBs may be included in the coverage1301 of a macro cell configured by macro eNBs.

As indicated by a reference “1305”, the coverages 1302 of a pluralityof, for example, “two”, small cells may be included in the coverage 1301of one macro cell. The user equipment (UE) 1303 is included in thecoverage 1302 of a small cell, for example, and performs communicationthrough the small cell.

In the configuration of a cell illustrated in FIG. 7, as indicated by areference “1306”, the coverage 1301 of a macro cell configured by macroeNBs and the coverage 1302 of a small cell configured by small eNBs mayoverlap each other in a complicated manner.

Further, as indicated by a reference “1307”, there also occurs a casewhere the coverage 1301 of a macro cell configured by macro eNBs and thecoverage 1302 of a small cell configured by small eNBs may not overlapeach other.

Further, as indicated by a reference “1308”, the coverage 1302 of alarge number of small cells configured by a large number of small eNBsmay be configured in the coverage 1301 of one macro cell configured byone macro eNB.

The problems solved and a solution in the first embodiment will bedescribed below. In the present embodiment, considered here is aconfiguration that a coverage of small cells configured by small eNBs isincluded in the coverage of a macro cell configured by macro eNBs.

As described above, in order to satisfy an enormous traffic in thefuture, examples of the study include the technique of increasingspectral efficiency through installation of a large number of smallcells by installing a large number of small eNBs to increase acommunication capacity.

In the case where a large number of small cells are installed, itbecomes a problem about to which small cell the UE is to be connected.

For example, considered here is a case where a small cell in whichreceived power in the UE becomes maximum is selected like theconventional technique. In this case, when the load of the selectedsmall cell is already excessively large, radio resources given to the UEconnected to the small cell are reduced, and high throughput cannot beobtained. Therefore, there occurs a problem such as the occurrence of ahigh delay in the data transmission.

In the present embodiment, in order to solve such a problem, inselecting a small cell to be connected to the UE, information about aflow of data (hereinafter, also referred to as a “data flow”) is used.Thus, it is an object to improve a delay in the entire network bydispersing the process load of a small cell.

FIG. 8 is a block diagram showing the configuration of the communicationsystem 1400 according to the first embodiment of the present invention.The communication system 1400 is configured to include a UE 1401, asmall cell cluster 1402, an MME 1403, an S-GW 1404, a macro cell 1406,and a concentrator 1407. The small cell cluster 1402 includes one or aplurality of small cells 1405.

The MME 1403 and the S-GW 1404 correspond to higher-level devices. Inthis case, the higher-level device refers to a device provided in ahigher level of the base station device. That is, the higher-leveldevice is provided on a core network side based on the base stationdevice. As the higher-level devices, there are a higher-level entity anda higher-level node.

The base station device is a macro eNB and a small eNB, for example, andconfigures a cell like a macro cell and a small cell. In the case wherea plurality of cells are installed, the plurality of cells may beconfigured by one base station device, or may be configured by aplurality of base station devices.

FIG. 8 illustrates a case where the small cell cluster 1402 includesthree small cells 1405. In the following description, in the case ofdistinctly indicating three small cells 1405, by adding suffixes “a”,“b”, and “c” to the reference “1405”, the small cells 1405 will berespectively indicated as a first small cell #1 1405 a, a second smallcell #2 1405 b, and a third small cell #3 1405 c. In the case ofindicating three small cells 1405 without distinction, the small cellwill be indicated by adding a reference “1405”.

The small cell 1405 is configured by a small eNB. The eNB thatconfigures the small cell 1405 corresponds to Home-eNB 75 illustrated inFIG. 2 described above, for example. The macro cell 1406 is configuredby a macro eNB. The macro eNB that configures the macro cell 1406corresponds to an eNB 76 illustrated in FIG. 2 described above, forexample.

The communication system 1400 according to the present embodiment isconfigured to include the concentrator 1407 between the macro cell 1406and the small cell 1405, unlike the architecture of the communicationsystem of the conventional technique. The concentrator 1407 is an entitythat collectively controls the small cells 1405 in the small cellcluster 1402 consisting of one or a plurality of small cells 1405.

The macro cell 1406 and the concentrator 1407 are connected to eachother by means of a new interface. The small cell 1405 and theconcentrator 1407 are connected to each other by means of a newinterface. A plurality of small cells 1405 are connected to oneconcentrator 1407. In the example illustrated in FIG. 8, three smallcells 1405 are connected to one concentrator 1407. The small cells 1405are connected to each other by means of an interface. In the case whereeach small cell is configured by one small eNB, an x2 interface is usedas an interface between the small cells 1405.

FIG. 9 is a diagram showing the flow direction of data in thecommunication system 1400 according to the first embodiment of thepresent invention. In FIG. 9, an uplink (UL) traffic is indicated by anarrow of a reference “41”, and a downlink (DL) traffic is indicated byan arrow of a reference “42”.

The concentrator 1407 has the function of obtaining a total of data flowin the small cell 1405 (hereinafter, also referred to as a “total dataflow”) regarding each small cell 1405 in the small cell cluster 1402 asthe own management item. Further, the concentrator 1407 has the functionof selecting the small cell 1405 to which the UE 1401 is connected.

Each small cell 1405 has the function of measuring a data flow in theown cell, and the function of notifying the measured data flow in theown cell to the concentrator 1407. It is preferable that when notifyingthe concentrator 1407 of the measured data flow in the own cell, eachsmall cell 1405 notifies the data flow together with the cellidentification information of the own cell. The cell identificationinformation of each small cell 1405 is useful when the concentrator 1407selects the small cell 1405.

As the data flow, for example, information expressing a size of data(hereinafter, also referred to as a “data size”) or an amount of data(hereinafter, also referred to as a “data amount”) of data handled ineach small cell 1405 may be used, and information expressing the datasize of the data handled by the transmission data buffer unit when eachsmall cell 1405 transmits the data to the UE 1401 may be used.

As detailed examples of the data flow concerning uplink of each smallcell 1405 (hereinafter, also referred to as an “uplink data flow”), thefollowing four examples (1) to (4) will be disclosed.

(1) The data size of the data that each small cell 1405 has transmittedto a higher-level entity or a higher-level node (hereinafter, alsoreferred to as “transmission data”).

(2) The data size of the data that each small cell 1405 has receivedfrom a lower-level entity or a lower-level node (hereinafter, alsoreferred to as “received data”).

(3) Buffer status report (BSR) information that each small cell 1405 hasreceived from the UE 1401 connected to the own cell 1405.

(4) Combination of the examples (1) to (3).

BSR information (hereinafter, also simply referred to “BSR”) indicates astate of a buffer unit that temporarily stores data transmitted from theUE 1401 to each small cell 1405. The buffer unit corresponds to thetransmission data buffer unit 803 illustrated in FIG. 3 described above.The BSR expresses a flow of received data.

More specifically, the BSR includes information expressing the data sizeof the data handled by the transmission data buffer unit of the UE 1401.Therefore, by using the BSR, it becomes possible to measure the uplinkdata flow of each small cell 1405.

In the present embodiment, each small cell 1405 has the function ofmeasuring the data flow. Therefore, in the detailed example (1) of theuplink data flow, the data size may be that of the data that the smallcell 1405 has transmitted to the concentrator 1407 being thehigher-level node. In the detailed example (2), because the lower-levelnode becomes the UE 1401, the data size may be that of the data that thesmall cell 1405 has received from the UE 1401 connected to the own cell1405. In the detailed example (3), the data size may be the BSRinformation that the small cell 1405 has received from the UE 1401connected to the own cell 1405.

In both the detailed examples (1) and (2), the data size may be that foreach UE 1401 connected to the small cell 1405, or may be a total datasize of all the UEs 1401 connected to the small cell 1405.

In the case of the data size of each UE 1401 connected to the small cell1405, the concentrator 1407 being the entity that obtains the data flowand selects the cell of a target UE 1401 may derive a total data size ofall the UEs 1401 connected to each small cell 1405. Accordingly, itbecomes possible to drive the data flow of each small cell 1405. In thiscase, because it becomes unnecessary for the small cell 1405 to derivethe total data size of all the UEs 1401, it becomes possible to simplifythe control.

In the case of the total data size of all the UEs 1401 connected to thesmall cell 1405, the concentrator 1407 being the entity that obtains thedata flow and selects the cell of the target UE 1401 may set the totaldata size as the flow of each small cell 1405. Because the small cell1405 notifies the total data size of all the UEs 1401 to be connected,as compared with the case of notifying the data size of each UE 1401, itbecomes possible to decrease a calculation volume of the concentrator1407.

Also in the detailed example (3), the data size may be the BSRinformation of each UE 1401 connected to the small cell 1405, or may bethe BSR information of all the UEs 1401 connected to the small cell1405. Accordingly, it becomes possible to obtain the effects similar tothose in the detailed examples (1) and (2).

The BSR information of all the UEs 1401 connected to the small cell 1405may be a list that expresses a correspondence between the BSRinformation of each UE 1401 and the identification information of the UE1401, for example the UE-ID, or may be an uplink data size derived fromthe BSR information of all the UEs 1401 that the small cell 1405 hasreceived.

Also, considered here is a case where a large number of small cells 1405are used and the UE 1401 is connected to a plurality of cells. In thiscase, like the conventional technique, when the BSR is notified to thecell to which the control plane (C-plane) is to be connected, in othercells to which the UE 1401 is connected, the data flow attributable tothe UE 1401 cannot be recognized.

In the present embodiment, the data size of each entity to which the UE1401 is connected, that is, the data size of each cell, or the BSR isnotified. The notification of the data size of each entity to which theUE 1401 is to be connected, or the BSR, may be performed on the entityor on the cell to which the control plane (C-plane) is to be connected.In the case where the notification is performed with respect to the cellto which the control plane (C-plane) is to be connected, for the datasize or the BSR, a list that expresses a correspondence between the cellidentification information and the data size or the BSR may be notified.

By configuring in this way, unlike the case where the BSR is notified toonly the cell to which the conventional control plane (C-plane) is to beconnected, even in the case where the UE 1401 is connected to aplurality of cells, the network side can recognize the data flow of eachentity, that is, each cell.

Further, the data size may be the data size or the BSR information inthe user plane (U-plane) connection.

In the case where a large number of small cells 1405 are used and the UE1401 is connected to a plurality of cells, unlike the conventionaltechnique, there is a case where the cell to which the control plane(C-plane) is to be connected and cell to which the user plane (U-plane)is to be connected are different.

Therefore, in the present embodiment, the data size or the BSRinformation specified for the entity or the node in the user plane(U-plane) connection is the data flow. Accordingly, it becomes possibleto measure the data flow in the user plane (U-plane) connection.

For the measurement of the data flow, the flow during a predeterminedperiod may be measured. As the predetermined period, a start time and aperiod may be set, or a start time and an end time may be set. Thepredetermined period may be statically predetermined, or may be setappropriately changeable semi-statically or dynamically. The data flowmay be a packet number, a bit number, or a byte number per apredetermined period. Alternatively, the data flow may be a packetnumber, a bit number, or a byte number per a unit time obtained from themeasurement of the data flow during a predetermined period. Change ofthe predetermined period may be performed by an instruction of theconcentrator 1407.

A node or an entity having the function of measuring the data flownotifies an entity or a node having the function of selecting the smallcell 1405 to which the target UE 1401 is to be connected, of theinformation about the data flow.

In the present embodiment, each small cell 1405 is the node having thefunction of measuring the data flow, and the concentrator 1407 is theentity having the function of selecting the small cell 1405 to which thetarget UE 1401 is to be connected. In this case, each small cell 1405notifies the concentrator 1407 of the information about the data flow.The concentrator 1407 receives the information about the data flow fromeach small cell 1405.

As detailed examples of trigger of notifying the information about thedata flow, the following three examples (1) to (3) will be disclosed.

(1) Cyclical or periodical.

(2) By providing a predetermined threshold value, in the case where thedata flow becomes equal to or higher than the threshold value, or in thecase where the data flow exceeds the threshold value.

(3) In the case where a request has been received from the entity havingthe function of selecting a small cell.

As the interface to be used to notify the information about the dataflow, a new interface may be provided between the small cell 1405 andthe concentrator 1407.

In order to decrease the information volume of the data flow, bydividing the data flow into one or a plurality of predetermined ranges,an index may be provided in each range. The index is set as informationabout the data flow. By such arrangement, it becomes possible todecrease the information volume notified between the nodes, such as thebit number, for example. Therefore, in the case where a large number ofsmall cells 1405 are applied, because the information volume signaledbetween the nodes can be reduced, it becomes possible to reducecongestion.

In FIG. 8 described above, a case where the BSR is used in the uplinkdata flow will be described (see Chapter 5.4.5 of 3GPP TS 36.321 V11.2.0(hereinafter, referred to as “Non-Patent Document 9”)). The BSR notifiedfrom the UE 1401 is terminated by the small cell 1405 in the standarddefined in Non-Patent Document 9.

The BSR is MAC information (see Non-Patent Document 9). According to theconventional base station, for example, the macro cell, a controlprotocol to the user equipment, for example, a radio resource control(RRC) and a user plane, for example, a packet data convergence protocol(PDCP), a radio link control (RLC), a medium access control (MAC), and aphysical layer (PHY) are terminated in the base station. Accordingly,the BSR being the MAC information also becomes the information from theuser equipment to the base station.

Therefore, according to the conventional method, in FIG. 8, the BSRbecomes the information from a UE 1401 to the small cell 1405 connectedto the UE 1401.

According to the conventional method, the entity other than the eNBbeing the base station directly connected to the UE 1401 cannot realizeselection of a connection cell based on the data flow of the cell.

Therefore, in the present embodiment, the BSR information is arranged tobe notified from the small cell 1405 to the concentrator 1407.

By using the data size of the transmission data notified from the BSR,the concentrator 1407 selects the small cell 1405 to which the UE 1401is to be connected.

The concentrator 1407 notifies the small cell 1405 to which the targetUE 1401 is currently connected, of the information of the selected smallcell 1405 as the information of the small cell 1405 to which the UE 1401is to be connected. The information of the selected small cell 1405 maybe notified together with the identifier of the target UE 1401.

The small cell 1405 to which the UE 1401 is currently connected receivesthe information of the small cell 1405 to which the target UE 1401 is tobe connected, and transmits an RRC reconfiguration message, so that theinformation of the small cell 1405 to be connected is notified to the UE1401.

The UE 1401 executes connection to the small cell 1405 which theconcentrator 1407 has selected, by using the received RRCreconfiguration message.

In the case where the RRC connection is not being performed between thesmall cell 1405 to which the UE 1401 is currently connected and the UE1401, the concentrator 1407 may notify the cell that has the RRCconnection with the UE 1401 of the information of the small cell 1405 towhich the UE 1401 is to be connected. The information of the small cell1405 to which the UE 1401 is to be connected may be notified togetherwith the identifier of the target UE 1401.

The cell that has the RRC connection with the UE 1401 receives theinformation of the small cell 1405 to which the target UE 1401 is to beconnected, and transmits an RRC reconfiguration message, so that theinformation of the small cell 1405 to be connected is notified to the UE1401.

For example, in the case where the cell that has the RRC connection withthe UE 1401 is the macro cell 1406, the concentrator 1407 notifies themacro cell 1406 of the information of the small cell 1405 to which theUE 1401 is to be connected. The macro cell 1406 receives the informationof the small cell 1405 to which the target UE 1401 is to be connected,and transmits the RRC reconfiguration message, so that the informationof the small cell 1405 to be connected is notified to the UE 1401.

The UE 1401 executes connection to the small cell 1405 which theconcentrator 1407 has selected, by using the received RRCreconfiguration message.

In the case where a connection destination has been notified for atarget cell of handover, the UE 1401 executes handover to the notifiedsmall cell 1405 to be connected.

In the case where a connection destination has been notified as asecondary cell of carrier aggregation, the UE 1401 configures thenotified small cell 1405 to be connected, as the secondary cell.

FIG. 10 is a diagram showing the configuration of the protocol stack inthe communication system 1410 according to the conventional technique.FIG. 11 is a diagram showing the configuration of the protocol stack inthe communication system 1400 according to the first embodiment of thepresent invention.

According to the macro cell 1406 being the conventional base station,the user plane terminates up to PDCP, that is, the PDCP, RLC, MAC, andPHY. On the other hand, in the present embodiment, the small cell 1405terminates the RLC, MAC, and PHY, and the macro cell 1406 terminates thePDCP.

The concentrator 1407 has the function of selecting the small cell 1405connected to the target UE 1401.

The BSR information is notified from the UE 1401 to the small cell 1405.The small cell 1405 further notifies the concentrator 1407 of the BSRinformation. For example, the BSR information is notified from the UE1401 to a third small cell #3 1405 c, and is notified from the thirdsmall cell #3 1405 c to the concentrator 1407.

Accordingly, the concentrator 1407 can obtain an uplink data flow ofeach small cell 1405, and can select the small cell 1405 to be connectedto the target UE 1401, by using the uplink data flow.

The uplink data from the target UE 1401 is to be transmitted to themacro cell 1406 through the small cell 1405 selected by the concentrator1407. For example, in the case where the small cell 1405 selected by theconcentrator 1407, to be connected to the target UE 1401 is the firstsmall cell #1 1405 a, the uplink data from the UE 1401 is transmitted tothe macro cell 1406 through the first small cell #1 1405 a.

In this way, in selecting the small cell 1405 to be connected to the UE1401, by using the information about the data flow, it becomes possibleto avoid selecting the small cell 1405 of a large uplink data flow, forexample. Accordingly, the process load of the small cell 1405 can bedispersed. Therefore, it becomes possible to improve a delay in theentire network.

When the BSR has been received from the UE 1401, the small cell 1405 mayuse the difference between the Short BSR and the Long BSR, for decidingwhether the BSR is to be transmitted to the concentrator 1407.

For example, by including in the Short BSR the information of the dataamount of the transmission data of the DCCH, and by including in theLong BSR the information of the data amount of the transmission data ofthe DTCH, the small cell 1405 may notify only the information of theLong BSR to the concentrator 1407.

Accordingly, the concentrator 1407 can recognize the data amount of thetransmission data of the user plane (U-plane) from the information ofthe Long BSR, and can select the small cell 1405, by using the dataamount of the transmission data of the user plane (U-plane). Therefore,it becomes possible to decrease the data amount of communication betweenthe small cell 1405 and the concentrator 1407.

As detailed examples of trigger of notifying the information about thedata flow, in place of the above detailed examples (1) to (3), thefollowing method may be employed.

In FIG. 8 described above, when the concentrator 1407 has received theBSR, in the case where the small cell 1405 not transmitting the BSRexists during a predetermined time in the small cell cluster 1402 thatthe concentrator 1407 manages, the concentrator 1407 may inquire thesmall cell 1405 about the total data flow.

Accordingly, the concentrator 1407 can select the optimum small cell1405, after recognizing the data flow in the small cell 1405 included inthe small cell cluster 1402.

Further, the small cell 1405 may periodically transmit the BSR to theconcentrator 1407, regardless of presence or absence of the reception ofthe BSR from the UE 1401.

Next, as detailed examples of the data flow concerning downlink(hereinafter, also referred to as a “downlink data flow”) of each smallcell 1405, the following three examples (1) to (3) will be disclosed.

(1) A data size of the data that each small cell 1405 has received fromthe higher-level entity or the higher-level node.

(2) A data size of the data that each small cell 1405 has transmitted tothe lower-level entity or the lower-level node.

(3) Combination of the examples (1) and (2).

In the present embodiment, the small cell 1405 has the function ofmeasuring the data flow. Therefore, in the detailed example (1) of thedownlink data flow, the data size may be that of the data that the smallcell 1405 has received from the concentrator 1407 being the higher-levelnode. In the detailed example (2), because the lower-level node becomesthe UE 1401, the data size may be that of the data that the small cell1405 has transmitted to the UE 1401 connected to the own cell 1405.

In both the detailed examples (1) and (2), the data size may be that foreach UE 1401 connected to the small cell 1405, or may be a total datasize of all the UEs 1401 connected to the small cell 1405. This issimilar to the case of the uplink data flow.

The data size may be that in the user plane (U-plane) connection. Thisis similar to the case of the uplink data flow.

For the measurement period of the data flow, notification of the dataflow, trigger of notification of the data flow, the interface for thenotification of the data flow, and the like, the interface and the likedisclosed concerning the uplink can be appropriately applied. Byappropriately applying in this way the interface and the like disclosedconcerning uplink, the effect similar to that in the case of uplink canbe obtained.

In FIG. 8, as the downlink data flow, a case where the data size of thedata transmitted to the lower-level entity or the lower-level node isused will be described.

The small cell 1405 measures a data size of the data transmitted fromthe own cell 1405 to the UE 1401 to be connected to the own cell 1405,and notifies the concentrator 1407 of the measured data size of the datatransmitted to the UE 1401. The concentrator 1407 selects the small cell1405 to which the target UE 1401 is to be connected, by using thedownlink data flow of each small cell 1405 in the small cell cluster1402 that the concentrator 1407 manages.

As the method for the concentrator 1407 to notify the target UE 1401 ofthe small cell 1405 which has been selected as the small cell 1405 towhich the UE 1401 is to be connected, it is possible to apply the methoddisclosed by the method of notifying the uplink data flow.

In the case where a connection destination has been notified for atarget cell of handover, the UE 1401 executes handover to the notifiedsmall cell 1405 to be connected.

In the case where a connection destination has been notified as asecondary cell of the carrier aggregation, the UE 1401 configures thenotified small cell 1405 to be connected as the secondary cell.

The entity having the function of selecting the small cell 1405 to whichthe target UE 1401 is to be connected may select the small cell 1405, byusing both the uplink data flow and the downlink data flow, or by usingone of the data flow. By using both the uplink data flow and thedownlink data flow, in the case where the target UE 1401 performsbidirectional communication, it becomes possible to select the optimumsmall cell 1405.

In the case where the link that is required to have high throughput andthe like to the target UE 1401 is one of uplink and downlink, the smallcell 1405 may be selected by using the data flow of one link.Accordingly, it becomes possible to select the small cell 1405 that isoptimum for communication of the UE 1401.

The entity having the function of measuring the data flow may notify theentity having the function of selecting the small cell 1405 to which thetarget UE 1401 is connected, of the uplink data flow and the downlinkdata flow together. The data flow of each link may be notified in thelist format, or may be a total value. Accordingly, it becomes possibleto decrease the message volume to be notified.

The small cell 1405 to which the UE 1401 is to be connected may beselected independently of uplink and downlink. By using the uplink dataflow and the downlink data flow in uplink and downlink respectively, itbecomes possible to select the optimum small cell 1405 in each link.

For example, the small cells 1405 in the small cell cluster 1402 areconfigured by the same frequency band and the same TAG. In the case ofselecting the small cell 1405 to which the target UE 1401 is connectedin the small cell cluster 1402, the small cell 1405 to which the UE 1401is connected may be different between downlink (DL) and uplink (UL). Theconcentrator 1407 executes selection of the small cell 1405independently of downlink (DL) and uplink (UL).

Because the small cells 1405 in the small cell cluster 1402 areconfigured by the same frequency band and the same TAG, transmissiontimings in uplink to the small cell 1405 selected in downlink become thesame. Therefore, even when any small cell 1405 is used in uplink, it isnot necessary to change the transmission timing, and it becomes possibleto simplify the control in the UE 1401.

Further, in both uplink and downlink, because the optimum small cell1405 can be selected, it becomes possible to realize high throughput anda low delay in both links.

For example, the small cells 1405 in the small cell cluster 1402 areconfigured by the same TA (Tracking Area). In the case of selecting thesmall cell 1405 to which the target UE 1401 is connected in the smallcell cluster 1402, the small cell 1405 to which the UE 1401 is connectedmay be different between downlink (DL) and uplink (UL). The concentrator1407 executes selection of the small cell 1405 independently of downlink(DL) and uplink (UL). Because the small cells 1405 in the small cellcluster 1402 are configured by the same TA and TAC, it is not necessaryto execute the procedure of TAU (Tracking Area Update), and it becomespossible to simplify the control.

In the function of selecting the small cell 1405 to which the UE 1401 isto be connected, as detailed examples of information used for theselection, the following five examples (1) to (5) will be disclosed.

(1) Data flow

(2) Load

(3) Communication quality

(4) Quality of service (QoS)

(5) Combination of the examples (1) to (4).

In selecting the cell, a load state of the small cell 1405 andcommunication quality may be considered. Considered here is a case wheretransfer load is high because communication quality is low although theflow is small.

In selecting the cell, the QoS required in the data may be considered.For example, as the data that is required to have a lower packet errorloss rate as the QoS, the small cell 1405 of high communication qualitymay be selected.

The data flow in the detailed example (1) described above includes atleast either one of the uplink data flow and the downlink data flow.Because this has been described above, the description will be omittedhere.

The load in the detailed example (2) described above includes a datadelivery delay time, throughput, the number of UEs 1401 connected to thesmall cell 1405, a using rate of the CPU (Central Processing Unit), ausing rate of radio resources, and a buffer stay amount in at leasteither one of the uplink data and the downlink data, for example.

Each small cell 1405 has the function of measuring the load, and eachsmall cell 1405 notifies the concentrator 1407 of the information aboutthe load (hereinafter, also referred to as “load information”). Theconcentrator 1407 receives the load information from each small cell1405. The concentrator 1407 selects the small cell 1405 to which thetarget UE 1401 is to be connected, by using the notified loadinformation.

For the measurement period of load, notification of load information,the trigger of notification of the load information, the interface forthe notification of the load information, and the like, the methoddisclosed concerning the data flow can be appropriately applied.Accordingly, it becomes possible to obtain the effects similar to thosein the method disclosed concerning the data flow.

As detailed examples of communication quality in the detailed example(3) above, the following nine examples (3-1) to (3-9) will be disclosed.

First, concerning downlink, the following four examples (3-1) to (3-4)will be disclosed.

(3-1) The number of times of ACK/NACK of the HARQ to the downlink data

(3-2) The number of times of ACK/NACK of the RLC to the downlink data

(3-3) CQI

(3-4) CSI

Next, concerning uplink, the following five examples (3-5) to (3-9) willbe disclosed.

(3-5) The number of times of ACK/NACK of the HARQ to the uplink data

(3-6) The number of times of ACK/NACK of the RLC to the uplink data

(3-7) The received power of the sounding reference signal (SRS)transmitted from the UE to the small cell

(3-8) Reception quality of the PUCCH. This may be the reception qualityof the DM-RS of the PUCCH.

(3-9) Reception quality of the PUSCH. This may be the reception qualityof the DM-RS of the PUSCH.

The number of times of ACK/NACK of the HARQ to the downlink data, theCQI, and the CSI are the information that the physical layer provides tothe MAC layer (see Chapter 4.3.2 of Non-Patent Document 9). The MACoperates the HARQ (see Chapter 5.3.2 of Non-Patent Document 9).

According to the conventional base station, for example, in the macrocell, a control protocol to the user equipment, for example, a radioresource control (RRC) and a user plane, for example, a packet dataconvergence protocol (PDCP), a radio link control (RLC), a medium accesscontrol (MAC), and a physical layer (PHY) terminate in the base station.Accordingly, the number of times of ACK/NACK of the HARQ to the downlinkdata, the CQI, and the CSI being the information that the physical layerprovides to the MAC layer also become the information from the userequipment to the base station.

Therefore, the number of times of the ACK/NACK of the RLC becomes theinformation of the base station that terminates the RLC protocol.

The number of times of ACK/NACK to the uplink data of the HARQ that theMAC operates becomes the information of the base station.

The received power of a sounding reference signal (SRS), the receptionquality of the PUCCH, and the reception quality of the PUSCH, being themeasurement information of the reception quality of the radio sections,become the information of the base station.

Therefore, according to the conventional method, it is impossible forthe entity other than the eNB being the base station directly connectedto the UE 1401 to realize the selection of the connection cell based onthe communication quality.

Then, in the present embodiment, the small cell 1405 notifies the entityor the node having the function of selecting the small cell 1405 towhich the target UE 1401 is to be connected, of the communicationquality.

The entity or the node having the function of selecting the small cell1405 to which the target UE 1401 is connected, selects the small cell1405 to which the UE 1401 is to be connected, by using the notifiedcommunication quality.

For the measurement period of communication quality, notification ofcommunication quality information, trigger of notification of thecommunication quality information, the interface for the notification ofthe communication quality information, and the like, the methoddisclosed concerning the data flow can be appropriately applied.Accordingly, it becomes possible to obtain the effects similar to thosein the method disclosed concerning the data flow.

As detailed examples of the QoS in the detailed example (4) describedabove, the following six examples (4-1) to (4-6) will be disclosed.

(4-1) QoS class identifier (QCI)

(4-2) Allocation and retention priority (ARP)

(4-3) Guaranteed bit rate (GBR)

(4-4) Maximum bit rate (MBR)

(4-5) Packet delay

(4-6) Packet error loss rate

The entity having the QoS information notifies the entity having thefunction of selecting the small cell 1405 to which the target UE 1401 isto be connected, of the information of the QoS.

For the notification of the QoS information, trigger of notification ofthe QoS information, the interface for the notification of the QoSinformation, and the like, the method disclosed concerning the data flowcan be appropriately applied. Accordingly, it becomes possible to obtainthe effects similar to those in the method disclosed concerning the dataflow.

In the detailed example (5) described above, the small cell 1405 mayhave the function of measuring the data flow by the combination of thepieces of information.

The small cell 1405 may notify the concentrator 1407 of the pieces ofinformation at different timings, or may notify one or a plurality ofpieces of information at the same timing.

Further, the concentrator 1407 may select the small cell 1405 to whichthe target UE 1401 is to be connected, by using a part or the whole ofthe information received from each small cell 1405.

Accordingly, depending on the wave environment between the target UE1401 and the small cell 1405 in the small cell cluster 1402, it becomespossible to appropriately change the small cell 1405 to be selected.Therefore, it becomes possible to select the optimum small cell 1405.

By employing the method disclosed in the present embodiment while theconcentrator 1407 uses the information about the data flow whenselecting the small cell 1405 to be connected to the UE 1401, it becomespossible to disperse the process load of the small cell 1405. Therefore,it becomes possible to improve a delay in the entire network.

When the concentrator 1407 selects the small cell 1405 to be connectedto the UE 1401, it becomes possible to use other various pieces ofinformation, and becomes possible to select the small cell 1405 which ismore optimum for communication. Accordingly, communication with highthroughput and a low delay becomes possible.

As described above, according to the present embodiment, the small cell1405 to which the UE 1401 is to be connected is selected from among aplurality of small cells 1405, based on the flow of at least either oneof the received data that each small cell 1405 receives from the UE 1401and the transmission data that each small cell 1405 transmits to the UE1401. Accordingly, in the case where the traffic volume in thecommunication system 1400 has increased, load can be dispersed to eachcell 1405 that configures the small cell cluster 1402. Therefore,because concentration of traffic in a specific small cell 1405 can beprevented, it is possible to reduce the occurrence probability of adelay in the network and loss of data.

In the present embodiment, the communication system 1400 includes theconcentrator 1407. The concentrator 1407 selects the small cell 1405 towhich the UE 1401 is to be connected from among a plurality of the smallcells 1405, based on the flow of at least either one of the receiveddata that each small cell 1405 receives from the UE 1401 and thetransmission data that each small cell 1405 transmits to the UE 1401.

By providing the concentrator 1407, it becomes possible to realize, in asimple configuration, the communication system 1400 capable of reducingthe occurrence probability of a delay in the network and loss of data asdescribed above.

In the present embodiment, the flow of the received data is expressed bythe BSR information. The BSR information is transmitted from the UE 1401to the small cell 1405, and is also transmitted from the small cell 1405to the concentrator 1407 or other higher-level device. The concentrator1407 or other higher-level device that has received the BSR informationfrom the small cell 1405 selects the small cell 1405 to which the UE1401 is to be connected, from among a plurality of small cells 1405,based on the BSR information.

By selecting the small cell 1405 that the UE 1401 is to be connectedbased on the BSR information in this way, it becomes possible to selectthe small cell 1405 which is more optimum for communication.Accordingly, communication with high throughput and a low delay becomespossible.

Further, in the present embodiment, the communication system 1400includes the macro cell 1406 and a plurality of the small cells 1405.From among a plurality of small cells 1405, the small cell 1405 to whichthe UE 1401 is to be connected is selected based on the flow of at leasteither one of the received data and the transmission data of each smallcell 1405. Accordingly, in the case where a large number of small cells1405 are installed, the process load can be properly dispersed to eachsmall cell 1405. Therefore, it becomes possible to more securely improvea delay in the entire network.

First Embodiment Modification 1

In the example disclosed in the first embodiment, the small cell 1405has the function of measuring the data flow. In the presentmodification, the concentrator 1407 has the function of measuring thedata flow of each small cell 1405.

In this case, concerning uplink, the data size of the data received fromeach small cell 1405 being the lower-level entity may be measured.Concerning downlink, the data size of the data transmitted to each smallcell 1405 being the lower-level entity may be measured. By sucharrangement, the concentrator 1407 can measure the data flow of eachsmall cell 1405.

By arranging such that the concentrator 1407 has the function ofmeasuring the data flow of each small cell 1405, it becomes possible tomake the entity of measuring the data flow the same as the entity ofselecting the small cell 1405 to be connected to the UE 1401.

Accordingly, because it becomes unnecessary for each small cell 1405 tonotify the concentrator 1407 of a measured result of the data flow, itbecomes possible to decrease the signaling volume. Further, becausemeasurement and selection can be unified in the concentrator 1407, ameasurement timing can be flexibly configured. Therefore, it becomespossible to select more timely a dynamic small cell 1405.

First Embodiment Modification 2

In the example disclosed in the first embodiment, the concentrator 1407has the function of selecting the small cell 1405 to which the UE 1401is to be connected. In the present modification, the macro cell 1406 hasthe function of selecting the small cell 1405 to which the UE 1401 is tobe connected.

In this case, the entity having the function of measuring the data flownotifies the macro cell 1406 of the data flow of each small cell 1405.The macro cell 1406 obtains the data flow of each small cell 1405. Themacro cell 1406 selects the small cell 1405 to be connected to the UE1401, by using the data flow of each small cell 1405.

The macro cell 1406 notifies the UE 1401 of the information of theselected small cell 1405. This information may be notified through thesmall cell 1405 connected to the concentrator 1407 and the UE 1401, andwhen the UE 1401 is connected to the macro cell 1406, the informationmay be directly notified from the macro cell 1406 to the UE 1401. Forthe method of notification from the small cell 1405 or the macro cell1406 to the UE 1401, the method disclosed in the first embodiment can beapplied.

For example, in the case where each small cell 1405 has the function ofmeasuring the data flow of the own cell 1405, each small cell 1405 maynotify the measured data flow of the own cell 1405 to the macro cell1406 through the concentrator 1407.

By such arrangement, it becomes unnecessary to increase the function ofthe concentrator 1407. Therefore, in the case of configuring theconcentrator 1407 separately from the macro cell 1406, it becomespossible to facilitate the configuration of the concentrator 1407.

First Embodiment Modification 3

According to the example disclosed in the first embodiment, in the userplane (U-plane) connection between the UE 1401 to be connected to thesmall cell 1405 and the S-GW 1404, the S-GW 1404 is connected to theconcentrator 1407 through the macro cell 1406.

In the present modification, in the user plane (U-plane) connectionbetween the UE 1401 to be connected to the small cell 1405 and theS-GW1404, the S-GW1404 is directly connected to the concentrator 1407.Accordingly, the S-GW1404 and the small cell 1405 are connected to eachother through the concentrator 1407 without through the macro cell 1406.

Therefore, because the user plane (U-plane) data handled in the smallcell 1405 does not pass through the macro cell 1406, it becomes possibleto decrease the process in the macro cell 1406.

In this case, the concentrator 1407 may have the PDCP to the UE 1401, orthe small cell 1405 may have the PDCP.

Second Embodiment

FIG. 12 is a block diagram showing the configuration of a communicationsystem 1500 according to a second embodiment of the present invention.The communication system 1500 according to the present embodiment isconfigured to include an UE 1501, a small cell cluster 1502, an MME1503, an S-GW 1504, and a macro cell 1506.

The small cell cluster 1502 includes one or a plurality of small cells1505. FIG. 12 illustrates a case where the small cell cluster 1502includes three small cells 1505.

In the following description, in the case of distinctly indicating threesmall cells 1505, by adding suffixes “a”, “b”, and “c” to the reference“1505”, the small cells 1505 will be respectively indicated as a firstsmall cell #1 1505 a, a second small cell #2 1505 b, and a third smallcell #3 1505 c. In the case of indicating three small cells 1505 withoutdistinction, the small cell will be indicated by adding a reference“1505”.

In the first embodiment, as illustrated in FIG. 8, the concentrator 1407is configured separately from the macro cell 1406. On the other hand, inthe present embodiment, the macro cell 1506 has the function of aconcentrator 1507 as well. That is, the macro cell 1506 includes theconcentrator 1507.

The function of the concentrator 1507 is the function of collectivelycontrolling the small cells 1505 in the small cell cluster 1502including one or a plurality of small cells 1505, in a similar manner tothat of the concentrator 1407 disclosed in the first embodiment.

In the present embodiment, the function of the concentrator 1507 isadded to the macro cell 1506. The user plane (U-plane) connectionbetween the UE 1501 to be connected to the small cell 1505 and the S-GW1504 is performed through the macro cell 1506.

The macro cell 1506 has the function of obtaining the data flow and thefunction of selecting the small cell 1505 to which the UE 1501 is to beconnected, for each small cell 1505 in the small cell cluster 1502 beingthe management item of the function of the concentrator 1507 that themacro cell 1506 has.

Each small cell 1505 has the function of measuring the data flow, andthe function of notifying the macro cell 1506 having the function of theconcentrator 1507, of the measured data flow.

In the configuration illustrated in FIG. 12, by appropriately employingthe method disclosed in the first embodiment while the macro cell 1506uses the information about the data flow when selecting the small cell1505 to be connected to the UE 1501, it becomes possible to disperse theprocess load of the small cell 1505. Therefore, it becomes possible toimprove a delay in the entire network.

When the macro cell 1506 selects the small cell 1505 to be connected tothe UE 1501, it becomes possible to use other various pieces ofinformation, and becomes possible to select the small cell 1505 which ismore optimum for communication. Accordingly, communication with highthroughput and a low delay becomes possible.

Further, in the case where the UE 1501 is connected to not only one ormore small cells 1505 but also to the macro cell 1506, the macro cell1506 can select the small cell 1505 to be connected to the UE 1501.Accordingly, it becomes possible to put together in the macro cell 1506the control to the UE 1501. Therefore, it becomes possible to reducemalfunction.

The macro cell 1506 having the function of the concentrator 1507 mayhave the function of measuring the data flow of each small cell 1505.

In this case, concerning uplink, the data size of the data received fromeach small cell 1505 being the lower-level entity may be measured.Concerning downlink, the data size of the data transmitted to each smallcell 1505 being the lower-level entity may be measured.

By such arrangement, the macro cell 1506 can measure the data flow ofeach small cell 1505. Accordingly, because it becomes unnecessary foreach small cell 1505 to notify the macro cell 1506 of a measured resultof the data flow, it becomes possible to decrease the signaling volume.Therefore, it becomes possible to obtain the effects similar to those inthe first embodiment.

In the present embodiment, as illustrated in FIG. 12, the user plane(U-plane) connection between the UE 1501 to be connected to the smallcell 1505 and the S-GW 1504 is performed through the macro cell 1506.

In the user plane (U-plane) connection between the UE 1501 to beconnected to the small cell 1505 and the S-GW 1504, the S-GW 1504 may bedirectly connected to the small cell 1505. In this case, the S-GW 1504is connected to the small cell 1505 without through the macro cell 1506.

Therefore, because the user plane (U-plane) data handled in the smallcell 1505 does not pass through the macro cell 1506, it becomes possibleto decrease the process in the macro cell 1506. In this case, the smallcell 1505 may have the PDCP to the UE 1501.

In the user plane (U-plane) connection between the UE 1501 to beconnected to the small cell 1505 and the S-GW1504, in the case where theS-GW1504 is directly connected to the small cell 1505, the S-GW 1504 mayhave the function of measuring the data flow of each small cell 1505.

In this case, concerning uplink, the data size of the data received fromeach small cell 1505 being the lower-level entity may be measured.Concerning downlink, the data size of the data transmitted to each smallcell 1505 being the lower-level entity may be measured.

By such arrangement, the S-GW 1504 can measure the data flow of eachsmall cell 1505.

The S-GW 1504 notifies the entity that selects the small cell 1505 to beconnected to the UE 1501, of the measured data flow of each small cell1505. For example, in the case where the entity that selects the smallcell 1505 to be connected to the UE 1501 is the macro cell 1506, theS-GW1504 notifies the macro cell 1506 of the data flow. The S-GW 1504may notify the macro cell 1506 of the data flow through the MME 1503.

Accordingly, because it becomes unnecessary for the small cell 1505 tonotify the macro cell 1506 of a measured result of the data flow, itbecomes possible to decrease the signaling volume between the small cell1505 and the macro cell 1506.

As described above, according to the present embodiment, the macro cell1506 has the function of the concentrator 1507. Accordingly, because itbecomes unnecessary for each small cell 1505 to notify the macro cell1506 of a measured result of the data flow, it becomes possible todecrease the signaling volume. Therefore, it is possible to furtherimprove a delay in the entire network.

Third Embodiment

FIG. 13 is a block diagram showing the configuration of a communicationsystem 1600 according to a third embodiment of the present invention.The communication system 1600 according to the present embodiment isconfigured to include a UE 1601, a small cell cluster 1602, an MME 1603,and an S-GW 1604. The small cell cluster 1602 includes one or aplurality of small cells 1605. FIG. 13 illustrates a case where thesmall cell cluster 1602 includes three small cells 1605.

In the following description, in the case of distinctly indicating threesmall cells 1605, by adding suffixes “a”, “b”, and “c” to the reference“1605”, the small cells 1605 will be respectively indicated as a firstsmall cell #1 1605 a, a second small cell #2 1605 b, and a third smallcell #3 1605 c. In the case of indicating three small cells 1605 withoutdistinction, the small cell will be indicated by adding a reference“1605”.

In the second embodiment, as illustrated in FIG. 12, the macro cell 1506has the function of the concentrator 1507 as well. On the other hand, inthe present embodiment, the MME 1603 has the function of a concentrator1607 as well. That is, the MME 1603 includes the concentrator 1607.

The function of the concentrator 1607 is the function of collectivelycontrolling the small cells 1605 in the small cell cluster 1602including one or a plurality of small cells 1605, in a similar manner tothat of the concentrator 1407 disclosed in the first embodiment.

In the present embodiment, the function of the concentrator 1607 isadded to the MME 1603. The MME 1603 is directly connected to each smallcell 1605. Further, the S-GW1604 is directly connected to each smallcell 1605.

The MME 1603 has the function of obtaining the data flow and thefunction of selecting the small cell 1605 to which the UE 1601 is to beconnected, for each small cell 1605 in the small cell cluster 1602 beingthe management item of the function of the concentrator 1607 that theMME 1603 has.

Each small cell 1605 has the function of measuring the data flow, andthe function of notifying the MME 1603 having the function of theconcentrator 1607, of the measured data flow.

In the present embodiment, in the configuration illustrated in FIG. 13,the method disclosed in the first embodiment may be appropriately used.The MME 1603 may notify the UE 1601 of the information of the selectedsmall cell 1605, through the small cell 1605 connected to the UE 1601.

By such arrangement, when the MME 1603 selects the small cell 1605 to beconnected to the UE 1601, it becomes possible to use the informationabout the data flow. Accordingly, the process load of the small cell1605 can be dispersed. Therefore, it is possible to improve a delay inthe entire network.

When the MME 1603 selects the small cell 1605 to be connected to the UE1601, it becomes possible to use other various pieces of information,and becomes possible to select the small cell 1605 which is more optimumfor communication. Accordingly, communication with high throughput and alow delay becomes possible.

Because the MME 1603 has the function of selecting the small cell 1605to be connected to the UE 1601, the information of the small cell 1605to be connected to the UE 1601 can be directly notified to the S-GW1604.Therefore, a signaling volume required by the network side can be small.

Further, after the MME 1603 has selected the small cell 1605 to whichthe UE 1601 is to be connected, the S-GW1604 can perform with alow-level delay time the routing of data to one or more small cells 1605to which the UE 1601 is to be connected. Therefore, it becomes possibleto flexibly change the small cell 1605 to which the UE 1601 is to beconnected with a lower delay. Therefore, it becomes possible to selectthe small cell 1605 corresponding to the continuously changingsurrounding wave environment.

According to the first embodiment to the third embodiment describedabove, one small cell cluster 1402, 1502, or 1602 exists in thecommunication system 1400, 1500, or 1600. The number of small cellclusters 1402, 1502 and 1602 that exist in the communication systems1400, 1500, and 1600 is not limited to one. In the communication systems1400, 1500, and 1600, a plurality of small cell clusters 1402, 1502, and1602 may exist.

In the case where a plurality of small cell clusters 1402, 1502, and1602 exist in the communication systems 1400, 1500, and 1600, aplurality of concentrators 1407, 1507, and 1607 are configuredcorresponding to the small cell clusters 1402, 1502, and 1602. In thiscase, by applying the method disclosed in each embodiment, it ispossible to select the concentrators 1407, 1507, and 1607 that controlthe small cells 1405, 1505, and 1605 to be connected to the UEs 1401,1501, and 1601.

For example, considered here is a case where the macro cell 1406 isconnected to the concentrator 1407 corresponding to each small cellcluster 1402, like the first embodiment illustrated in FIG. 8. In thiscase, the macro cell 1406 is configured to have the function ofobtaining the data flow in each small cell cluster 1402, and thefunction of selecting to which small cell 1405 in the small cell cluster1402 the UE 1401 is to be connected.

Further, in this case, each small cell cluster 1402 is configured tohave the function of measuring the data flow, and the function ofnotifying the macro cell 1406 of the measured data flow, through theconcentrator 1407.

Without being limited to the above, by providing each small cell 1405with the function of measuring the data flow, each small cell 1405 maynotify the small cell cluster 1402 to which the UE 1401 is connected, ofthe measured data flow. Each small cell cluster 1402 derives the dataflow of the entire small cells 1405 belonging to the own cluster.

In the above configuration, by appropriately employing the methoddisclosed in the first embodiment while the macro cell 1406 uses theinformation about the data flow of each small cell cluster 1402 whenselecting the small cell 1405 to be connected to the UE 1401, it becomespossible to disperse the process load of the small cell cluster 1402.Therefore, it becomes possible to improve a delay in the entire network.

The embodiments and the modifications thereof described above are merelyexemplifications of the present invention, and the embodiments and themodifications thereof can be freely combined without departing from thescope of the present invention. Further, an arbitrary component in theembodiments and the modifications thereof can be appropriately changedor omitted. Accordingly, by installing small eNBs configuring a smallcell, a communication system that obtains a high communication capacitycan be provided.

For example, according to another embodiment of the present invention,the communication system may be a communication system including acommunication terminal device, and one or a plurality of base stationdevices that perform radio communication with the communication terminaldevice. The communication system includes a plurality of cells that areconfigured by the one or the plurality of base station devices, andperform radio communication with the communication terminal device bybeing connected to the communication terminal device, and a higher-leveldevice that is provided in a higher level of the base station device. Acell to which the communication terminal device is to be connected isselected from among the plurality of cells, based on a flow of receiveddata that each cell has received from the communication terminal device.

Accordingly, as in the case with each of the embodiments and themodification thereof described above, when the traffic volume in thecommunication system has increased, the load can be dispersed to eachcell. Therefore, because concentration of traffic in a specific cell canbe prevented, it is possible to reduce the occurrence probability of adelay in the network and loss of data.

Further, according to still another embodiment of the present invention,the communication system may be a communication system including acommunication terminal device, and one or a plurality of base stationdevices that perform radio communication with the communication terminaldevice. The communication system includes a plurality of cells that areconfigured by the one or the plurality of base station devices, andperform radio communication with the communication terminal device bybeing connected to the communication terminal device, and a higher-leveldevice that is provided in a higher level of the base station device. Acell to which the communication terminal device is to be connected isselected from among the plurality of cells, based on a flow oftransmission data which each cell has transmitted to the higher-leveldevice.

Accordingly, as in the case with each of the embodiments and themodification thereof described above, when the traffic volume in thecommunication system has increased, the load can be dispersed to eachcell. Therefore, because concentration of traffic in a specific cell canbe prevented, it is possible to reduce the occurrence probability of adelay in the network and loss of data.

While the present invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of thepresent invention.

DESCRIPTION OF REFERENCE NUMERALS

1400, 1500, 1600 communication system, 1401, 1501, 1601 mobile terminal(UE), 1402, 1502, 1602 small cell cluster, 1403, 1503, 1603 MME, 1404,1504, 1604 S-GW, 1405, 1505, 1605 small cell, 1406, 1506 macro cell,1407, 1507, 1607 concentrator.

1. A communication system comprising: a communication terminal device;at least one base station device configured to provide a plurality ofcells that are configured to perform radio communication with thecommunication terminal device; and a concentrator configured to select aplurality of cells to which the communication terminal device is to beconnected from among the plurality of cells based on at least one of adownlink data flow of each of the plurality of cells and an unlink dataflow of each of the plurality of cells.
 2. The communication systemaccording to claim 1, wherein the plurality of cells to which thecommunication terminal device is to be connected are a cell for acontrol plane and a cell for a user plane, and the cell for the controlplane and the cell for the user plane are different from each other. 3.The communication system according to claim 1, wherein the plurality ofcells to which the communication terminal device is to be connected area cell for uplink and a cell for downlink, and the cell for uplink andthe cell for downlink are different from each other.
 4. Thecommunication system according to claim 3, wherein the cell for uplinkand the cell for downlink belong to a same cell cluster.
 5. Aconcentrator that is included in a communication system comprising acommunication terminal device and at least one base station deviceconfigured to provide a plurality of cells that are configured toperform radio communication with the communication terminal device,wherein the concentrator is configured to select a plurality of cells towhich the communication terminal device is to be connected from amongthe plurality of cells based on at least one of a downlink data flow ofeach of the plurality of cells and an uplink data flow of each of theplurality of cells.